1. Field of the Invention
The present invention relates to washers, and more particularly to rivet sealing washers.
2. Description of the Related Art
Rivets are a type of permanent mechanical fastener used for connecting parts through which holes are formed. There are a number of different types of rivets, including: solid rivets, semi-tubular rivets, blind rivets, drive rivets, flush rivets, friction-lock rivets, and self-pierce rivets. Solid and semi-tubular rivets have a head and a shaft, and the end of the shaft farthest from the head is referred to as the buck-tail. Blind rivets are composed of two parts: the rivet body and the setting mandrel. Like solid and semi-tubular rivets, the rivet body of a blind rivet has a head and a shaft; however, the rivet body is tubular and has a setting mandrel that passes through the center of the rivet body, such that the setting mandrel head is located at the end of the rivet shaft farthest from the rivet head, and the tip of the setting mandrel protrudes through the rivet head end of the rivet body.
To join two materials together, blind rivets are inserted through aligned holes in the two substrates, and the rivet head is held in place against the first of the two substrates while an opposing force is applied to the mandrel. The opposing force causes the mandrel head to deform the end of the rivet shaft, thereby forming a complete rivet. A line of the weakness is provided in the mandrel stem adjacent to the mandrel head allowing it to break off at a pre-determined setting force once the rivet has been formed.
Blind rivets display adequate performance when joining metal work-pieces under standard conditions. However, blind rivets are disadvantageous for implementations that require, for example, an airtight or watertight seal on the backside of the materials to be joined because air or water can seep around the remnant of the mandrel head, and thereby pass through the rivet body. Additionally, the mandrel head can also fall out of the rivet body, thereby creating an unobstructed passage for air or water to flow through the rivet body.
Blind rivets are also disadvantageous for many electro-mechanical applications because vibrations in the equipment can cause the mandrel head to loosen and rattle within the rivet body. Additionally, the mandrel head can also fall out of the rivet body, as discussed above, thereby causing problems with, or damage to, the electrical and/or mechanical equipment containing the blind rivet.
Some previous techniques have tried to address these significant disadvantages by using a flowable sealant, such as an epoxy resin, that may be disposed between the rivet body and the mandrel head, such that setting of the blind rivet compresses the sealant between the head of the mandrel and an inner surface of the rivet body to form a seal between the two surfaces. Disadvantageously, such a proposal requires that the epoxy resin be evenly distributed when the rivet is set, however, normal variation in the deformation of the rivet shaft by the mandrel head occurs from rivet to rivet, and can result in incomplete seal formation because the epoxy resin is not evenly distributed. Another disadvantage of this technique is that epoxy resins require special conditions in order to cure properly, which increases the complexity of the rivet setting process. For example, some epoxy resins require high temperature and/or a separate chemical such as an activator in order to cure. In view of the foregoing, it is clear that the most significant disadvantage of this proposal is that it requires specially designed rivets, which are difficult to manufacture. An end-user interested in using such rivets would need to place a custom order with a rivet supplier who would, in turn, need to re-tool a production line in order to produce the rivets. As a consequence, rivets of the proposed technique would be prohibitively expensive.
Therefore, there is a need in the art for a way to modify an existing rivet so as to provide an airtight and/or watertight seal when sealing a variety of different materials.